The last decade has witnessed a renewed interest in security and perimeter monitoring. Sensitive sites such as nuclear power plants, water treatment systems, oil pipelines, and military facilities, are consistently under the threat of perimeter breaching from unwanted intruders. Such facilities require around the clock monitoring by a fail safe system requiring minimum human intervention. Historically, perimeter monitoring has relied heavily on infrared sensors and cameras, heat and motion detectors, vibrational and seismic perturbations. However, these systems are relatively poor performers, mostly un-concealable and require extensive capital investment. A fiber-based intrusion detection system, either buried or wall-mounted along a perimeter, addresses these specific issues related to implementation, cost practicality, concealment and accuracy.
In most fiber-based intrusion detection systems, pulses of light are launched into an optical fiber, by way of an Optical Time Domain Reflectometer (OTDR). Minute impurities (<<λ) randomly distributed inside the fiber scatter light in all directions. The portion of this scattered light that is reflected back to the OTDR is known as Rayleigh backscattered signal. Fiber-based intrusion sensing, for the most part, relies on characterizing the different parameters embedded within that Rayleigh backscattered signal coming from the fiber.